A multi-layer printed circuit board is conventionally manufactured by first preparing a copper clad laminate for the inner layer by processing a copper foil on the copper clad laminate to form a printed circuit; then subjecting the above copper foil to a surface roughening treatment (generally comprising degreasing, followed by a soft etching process as exemplified by treatment with ammonium persulfate, sodium persulfate, cupric chloride, sulfuric acid-hydrogen peroxide system and the like, as well as an activating treatment); subsequently building an acicular film of copper oxide or cuprous oxide on top of the foil by a process such as blackening or browning; and bonding a copper clad laminate for the outer layer or copper foils in multiple layers with a material impregnated with a thermosetting resin (i.e. a "prepreg") to fabricate a multi-layer laminated board having a high adhesion strength.
Since electric continuity has to be established to each layer of the multi-layer laminated board manufactured in the above process, a through-hole plating on holes drilled through the board is required. However, the conventional method has had a drawback whereby penetration of the acid solution used in the catalyst treatment process for plating through-holes or penetration of the plating solution in the electroless copper plating process tends to dissolve the film made from copper oxide or cuprous oxide, thereby causing a phenomenon called "pink ring"(i.e. "haloing").
On the other hand, there is an alternative method in which a printed circuit is formed on a copper clad laminate using a copper foil that is pre-processed by surface roughening to eliminate the need for surface roughening as well as the oxide film forming processes required in the method described above, thereby providing a multi-layer printed circuit board. This method, however, has shortcomings such as inferior pattern resolution for the printed etching resist or the etching resist for ultra-violet exposure, which are associated with the surface roughness of the copper foil.
In order to correct the above shortcomings, the present inventors have recently developed a method for forming a uniform and acicular copper film with excellent adhesion strength using electroless copper plating (Japanese Patent Application Laid-Open No. 116176/1992 and International Patent Application No. PCT/JP96/03829). This technology enabled manufacturing of a copper clad laminate having a copper film with a high adhesion strength, without the aforementioned shortcomings.